Tafsir of Ad-Dhariyat 51:25

إذ دخلوا عليه فقالوا سﻼما

قال سﻼم

When they came in to him and said: "Salaman!'' He answered: "Salamun.''

وإذا حييتم بتحية فحيوا بٲحسن منها أو ردوها

When you are greeted with a greeting, greet in return with what is better than it, or return it equally. (4:86) So the Friend of Allah chose a better reply in return for their greeting, implementing Allah's command: Reciprocating the greeting with the term Salamun is stronger than the greeting using the term Salaman. The three angels; Jibril, Mika'il and Israfil came to Ibrahim in the image of handsome young wonderfully graceful men. This is why Ibrahim said,

قوم منكرون

You are a people unknown to me. Allah the Exalted said,